US 3585441 A
Description (OCR text may contain errors)
United States Patent 3,146,371 8/1964 McGinn 315/111 X 3,270,498 9/1966 LaRocca 313/63 X 3,370,198 2/1968 Rogers et a1. 315/111 Primary Examiner- Douglas Hart Attorneys-William G. Becker, Paul F. Prestia, Allen E.
Amgott, Henry W. Kaufmann, Frank L. Neuhauser and Oscar B. Waddell ABSTRACT: Gas to be accelerated to high velocity and ejected is first accelerated to velocity sufficient to cause compression and possible ionization when gas is directed against backwall or breech of main discharge chamber. Main discharge electrodes produce high-energy discharge through gas, accelerating it both by thermal expansion and by electromagnetic forces; gas is then discharged through conventional nozzle. Length of flow paths may be such that device is acoustically self-pulsing with continuously supplied gas pressure and electrical potential.
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AGENT SHOCK IONIZATION GAS ACCELERATOR BACKGROUND OF THE INVENTION 1. Field of the Invention This invention pertains to the art of accelerating gases by electric discharges.
2. Description of the Prior Art A particular virtue of electrical acceleration of gases is that its result is very readily controllable in that electricity is the form of energy perhaps most readily controllable. However, to avoid waste of the working substance, or propellant gas, it is desirable to shut off the flow of gas during the time when electrical energy is not to be added to it. Also, in the interest of maximum economy of apparatus, it is desirable that the source of energy for the main discharge be not turned on and off to control the production of, thrust, but that the source be continuously connected once turned on, and the production of thrust be controlled by the effective rate at which gas is fed into the intraelectrode space in which the main discharge may occur. This effective rate may be the same as the actual rate at which gas is fed; this will be true if the gas fed is all ionized either prior to introduction into the main discharge space, or by the main discharge source inself. However, as an altemative, the field in the main discharge space may be insufficient to break down unionized gas; and the efiective rate of a gas which is actually fed physically at a constant flow rate may be varied by varying the ionization produced in the gas prior to its entry into the main discharge space. Alternatively, the flow of gas into the main discharge chamber may be controlled by a rapidly acting valve to control the production of thrust.
Since the working substance is jettisoned in the operation of the device, it is desirable to use if for maximum effect by imparting the maximum feasible momentum to it. This requirement, in most instances, implies storage of available electrical energy for a period, followed by its rapid transfer into the gas over a shorter period. Thus even when substantially continuous action is desired, pulsating operation is still commonly required.
While ionization of the gas prior to entry into the main discharge path is desirable to insure uniform energy transfer from pulse to pulse, the auxiliary ionizing discharge commonly employed for this purpose requires additional equipment and adds an energy loss. Similarly, when a rapidly acting valve'is used to control the flow of gas by individual pulses, weight and a wearing part are added. I have invented a device which is capable of pulsed operation without the use of an auxiliary ionizing discharge, and without a valve to interrupt the flow of gas into pulses.
1 SUMMARY OF THE INVENTION Thebasic novel function of my invention is the acceleration of a quantity of gas to high, preferably supersonic velocity at which it is directed against the backwall or breech of a main discharge chamber. The impact of the gas against the backwall may ionize it, but in any event it will cause a sharp increase in.
pressure (and thus in density) of the gas which will permit of a high-energy electrical discharge between main discharge electrodes which, in the preferred embodiment, are constantly connected to a main pulse power supply, ready to discharge whenever a suitably conductive medium is provided between the main discharge electrodes. This discharge, both by raising the temperature of the gas and by electromagnetic forces which it produces, causes the ionized gas (substantially a plasma, or nearly completely ionized but macroscopically neutral gas) to be accelerated along an exit passage (which may be of any of the conventional forms of nozzle, etc.
The gas flow into the main discharge chamber may, of course, be controlled by a quick-acting valve; and reliance may be placed upon the initial pressure at which the gas is fed through expansion nozzles into the main discharge chamber to produce the required supersonic velocity. Alternatively, an
electrical discharge between triggeringelectrodes in a vestibular chamber adjacent to the main discharge chamber bay be used to accelerate the gas, with partial ionization. There is, however, one possible mode of operation of my invention which is peculiarly attractive for some applications, in which it is desired to operate the engine for a large number of pulses, with the supply of gas to the device being turned on at the beginning of the series of pulses, and turned off at the end by a valve which may be comparatively slow acting because it does not have to operate in a time comparable with a single pulse period. In this mode of operation, I rely upon an acoustic resonance analogous to the resonance of a closed-end resonator blown at the open end. The fundamental resonance period is determined by the time which elapses from the entry of a puff of gas, through jets or nozzles, into the main discharge chamber, at supersonic velocity, directed to the rear wall of the main discharge chamber, from which it is reflected and then accelerated by the main discharge. This creates a highpressure wave which passes the jets or nozzles, producing a back pressure which prevents further gas flow from the jets or nozzles until the high'pressure wave has been succeeded by a rarefaction, which marks the end of one resonance period, and permits the cycle to recur. The effectiveness of this mode of operation may be increased by making the vestibular chamber, from which the gas is fed through the jets or nozzles to the main discharge chamber, a resonator of the same period, so that the stopping of the flow from the nozzles will produce in the vestibular chamber a pressure wave which will move backward (with respect to the normal direction of forward gas flow) to walls at which it will be reflected forward, arriving at the nozzles coincidentally with the passage of the rarefaction in the main discharge chamber. This will produce a maximal pressure differential across the nozzles or jets, and will cause a maximal acceleration of gas through the nozzles. This particular mode of operation permits the device to function without a quick-acting valve to control gas flow during each pulse cycle, and has the obvious virtue that it permits pulsed operation without any mechanical moving parts in the apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 represents an embodiment of my invention in which the flow of gas into the apparatus is subjected to a preliminary discharge to accelerate it into the breech of the apparatus to compress it very highly by shock against the rear of the breech with possible shock ionization; and it is accelerated by a resulting heavy discharge between main electrodes surrounding the breech volume; and
FIG. 2 represents an embodiment of my invention in which the flow of gas into the apparatus is at sufficiently high pressure and temperature that expansion through a suitable nozzle produces supersonic velocity sufficient to cause its compression and possible ionization by shock on striking the rear of the breech, whence it is accelerated by a resulting electrical discharge.
DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 there is represented in axial section a nonconductive gas feed tube 10, which carries through an insulating base 12 to a chamber 14 propellant gas from a conventional source not shown. Chamber 14 is within a conductive body 16, and is connected by nozzles 18 to an initial acceleration chamber 20. Chamber 20 is formed in part by an insulating sleeve 22 and a conductive sleeve 24 which are coaxial with a central electrode 26 which is represented as mounted on body 16. The previously recited parts are supported from cylindrical inner main electrode 28; it is mechanically and electrically connected with domed nd 30 and inner main electrode 32. The tubular connection between 28 and 30 and 32 is pierced by axially symmetrical nozzles 34 which point generally to the left of the figure toward the breech formed by insulating base 12. Outer main electrode 36 surrounds the entire assembly, being coaxial therewith. The insulating materials may conveniently be ceramic, and the conductive parts may be of any suitable metal, such, for example, as copper, nickel or stainless steel.
A first, relatively low power, electrical energy source 40, represented symbolically as a battery 42 shunted by capacitor 44, is provided to produce an initial accelerating discharge between central electrode 26 and conductive sleeve 24. The symbolic representation is intended to represent a high-potential source of appreciable internal resistance whose output is stored so that it can provide for a short period a high-current discharge. More sophisticated devices of the art, such as a pulse-forming network, may replace the simple representation. A switching device represented by rectangle 46 is connected by conductor 48 to one side of source 40, and by conductor 50 to body 16 (and so to central electrode 26). Conductor 52 connects the other terminal of source 40 to conductive sleeve 24. Thus when switching device 46 is closed, the terminals of source 40 are connected to sleeve 24 and central electrode 26, producing between them a field which can produce through gas between them a discharge which by combined thermal expansion and electromagnetic forces accelerates a mass of gas to the right of the figure into the domed cavity 54 formed by the end 30 of inner main electrode 32, producing a pressure which causes the gas to be accelerated by expansion, through nozzles 34, to supersonic velocity. The direction of orientation of nozzles 34 causes a shock wave of this high-enthalpy gas to pass backward through space 56 lying between main electrodes 28 and 36 until it strikes insulating base 12, which forms the backwall or breech of the accelerator. The shock impact at 12 may cause the gas to become very highly ionized, and will at least greatly increase its density. A second higher power, electrical energy source 58, represented as a battery 60 60 shunted by a capacitor 62 is connected via conductor 64, switching device 66, a conductor 68, and by conductor 70 to outer main electrode 39 and inner main electrode 28, respectively. The presence of the highly comprised gas in the space 56 causes a heavy electrical discharge to occur through the gas. The combination of rebound from the breech, thermal expansion of the gas, electromagnetic forces produced by the discharge causes a gas pressure pulse to travel to the right, producing a shock at the entrance to nozzle 34, which backs up the nozzle into cavity 54, and, in a preferred form of the invention, is transmitted through 20 to nozzles 18, stopping further influx of gas into 20. The pulse of gas in 56 continues forward to the right ofthe figure, past the mouth of nozzle 34 into the space between inner main electrode 32 and outer main electrode 36. It will be observed that the contemplated mode of operation involves passage of the gas from nozzles 34 to breech end 12 without occurrence ofa discharge between the main electrodes 56 and 28. This may occur if the density of gas leaving nozzles 34 is too high; but may be avoided by reducing the pressure at which gas is fed through tube 10.
The functioning of switching devices 46 and 66 has not been discussed. In the simplest mode of operation, 46 may be used in pulsed operation to determine the rate at which pulses of gas are expelled through nozzle 34; and 66 may be used as a simple switch which is turned on at the beginning of use of the device, the shock wave action serving to switch successive discharges. Alternatively, 66 may be operated in pulses in synchronism with 46, and with proper phase relation so that it is closed slightly before the pulse of gas resulting from the functioning of46 reaches the breeck, and remains closed until the gas is accelerated from the device, when it opens ready for the next cycle of operation, both actions occurring when no current is flowing. Alternatively, both 46 and 66 may be used as simple switches to turn the device on at the beginning of a period of operation. For such mode of operation, the gas entering through tube may be supplied in pulses provided by a repetitively operated valve (such, for example, as the one disclosed in U.S. Pat. No. 3,20l,00l) connected in series with the source ofgas, not shown, previously referenced. An alternative mode of operation, not requiring a pulsing valve, em-
ploys a rate of gas influx through tube 10 such that the tinie required for buildup of a pressure such that source 40 can discharge through it is equal to the desired period between pulses. The backward pressure wave produced at orifices 18 by reflection from cavity 54, will tend to reduce the flow gas through 18. The pressure wave resulting from the much heavier discharge in 56 from source 58, fed back through nozzle 34 and reflected from 54 will sharply increase the back pressure on 18. However, when the pressure wave between main electrodes 28 and 36, in space 56, has passed nozzle 34, it will be followed by a rarefaction which will cause a reduction in pressure at orifices 18, causing the flow of gas to be markedly increased, and repeating the cycle described. The time relations have been given, rather than apparatus dimensions, since the gas velocity will depend upon the energy added to it, and the times of travel of the pulses of gas will depend upon this, and upon the volume of gas in a pulse. It is evident that when these time relations exist, chamber 20 is resonant at the frequency of operation of the device.
FIG. 2 represents in diametral section an embodiment ofmy invention having circular symmetry around an axis vertical in the figure as represented. A conductive metal base is provided with an entry canal 82 through which gas may be admitted at high pressure from a source not shown to a chamber 83 in a central electrode 84, so that it strikes the domed inside 86 of the chamber 83 and is reflected and expanded through nozzles 88, whence it is expanded into the space 90 between central electrode 84 and peripheral electrode 92. It moves backward (at supersonic speed because of the high pressure at which is has been supplied, and its expansion through nozzles 88) against breech 94. The shock of this impact causes the gas to become ionized and rebound forward, or upward (as represented). It is noted that breech 94 is separated by a gap 96, partly closed by insulating shim 98, from insulator 100. The tortuous path provided by the assembly represented prevents any sputtered metal or other material from forming a continuous conducting path across the insulation. The insulating materials 94 and may be of ceramics.
An electrical energy source 102 is represented connected across the electrodes 84 and 92. When a gas pulse strikes and rebounds from breech 94, becoming compressed in the process, source 102 discharges through the gas, accelerating it by both thermal and electromagnetic means upward to bell mouth 104, whence it is discharged. This action is accompanied by the following effect: The discharge of source 102 through gas already rebounding at supersonic speed produces a pressure shock wave which travels up space 90. During the time that this high pressure exists at the nozzles 88, the flow of gas from the source through canal 82 will be checked. When the high-pressure wave has passed nozzles 88, it will be followed by a rarefaction which will promote flow once more through canal 82 and nozzles 88, starting the cycle once more. While bell mouth 104 is somewhat tapered, it is unlikely to be perfectly matched acoustically to the space into which it discharges, and so it will also reflect a rarefaction down to nozzles 88. It is desirable that the location of nozzles 88 along the length of the space 90 be such that the rarefactions from the termination of the shock wave accelerated upwards from breech 94 and the rarefactions from mismatch at bell mouth 104 arrive in phase. Since it is evident that the chamber 83 approximates a Helmholtz resonator, albeit with Q somewhat impaired by nozzles 90, it is evident that the length of chamber 83 should be so chosen that the period of the pulsations in space 90, accompanied by coincidentally phased arrival of rarefactions at nozzles 88, will equal a resonant period of chamber 83. Thus the chamber will be resonant at the frequency of operation of the device. Because the length of time required to drive a mass of gas up space 90 from breech 94 to hell mouth 104 will necessarily depend upon the energyimparting characteristics of source 102, the requisite relations must be described, as for H6. 1, in time, rather than spatial, relations.
1. A gas accelerator comprising:
two electrodes having a space between them closed at one end by a breech;
means for discharging a charge of gas at supersonic velocity backward against the breech, there compressing it;
electrical energy source means connected between the said two electrodes to produce an electrical discharge through said charge of gas after it has been compressed, to accelerate it in the space between the said electrodes in a forward direction away from the said breech in which the therein said breech comprises a labyrinthine gap.
2. A gas accelerator comprising:
two electrodes having a space between them closed at one end by a breech;
means for discharging a charge of gas at supersonic velocity backward against the breech. there compressing it;
electrical energy source means connected between the said